1. Field of the Invention
The present invention relates to a hyperbranched polyamine and its use to exfoliate an inorganic clay into random form of nanosilicate platelets; wherein the hyperbranched polyamine as an exfoliating agent is prepared by polymerizing poly(oxypropylene)-triamine with diglycidyl ether of bisphenol-A (DGEBA) and a subsequent acidification step by inorganic acid; and the layered inorganic silicate clay can be completely exfoliated by hydrophilic ammonium-salt groups of the polyamine exfoliating agent. The present invention further relates to a method for producing nanosilicate platelets which can be extracted from the exfoliated clay.
2. Related Prior Arts
Basically, interlayer distances of the layered inorganic clay such as montmorillonite (MMT) or synthetic fluorinated mica (Mica), can be increased from 10 Å to 20 Å through ion exchange reaction of the organic quaternary ammonium salts, and thus monomers can access in and out. “Intercalation” is used to indicate that organic molecules are embedded in the inorganic aluminosilicate interlayers while the clay structure remains in the form of layer stack crystals with constant interlayer space distance; and “exfoliation” indicates that each layer of the inorganic layers is present in the random form. The “intercalated” clay by an ionic surfactant generally can be dispersed in monomers or polymers and through a mixing procedure or polymerization procedure to produce a distribution of singular nano layers in polymer nanocomposite materials.
Conventional intercalating agents such as 12-aminolauric acid, hexadecyl amine salt, octadecyl amine salt, bis(2-hydroxyethyl)methyl tallow alkyl ammonium chloride and other fatty alkyl amine salts, usually have low molecular weights and polar ammonium groups, and thus can exchange with the counter cations within the layered silicate clays. As a result, organic intercalating agents may be embedded and the hydrophobicity of the inorganic clay is promoted to facilitate exfoliation and affinity with monomers or polymers.
In addition, T. J. Pinnavaia (Michigan State University) found that diglycidyl ether of bisphenol-A (epoxy resin Epon828) can polymerize with MMT to form a nano-scaled polyether/clay composite by using the alkyl amine salt intercalant, CH3(CH2)n—NH3+. For different formulae of the intercalant, d spacing can be enlarged to 18.0 Å. The intercalated MMT can further polymerize with the epoxy resin at 75° C. to give an epoxy/clay material with d spacing 34.1 Å. The product is proved to perform better heat distortion temperature (HDT). This intercalant may regularly act from monolayer to bilayer, and further to pseudo-trimolecular, with an interlayer distance ranging from 13.8 to 18.0 Å. Within the layers of such width, the epoxy resin can enter and disperse the layered inorganic to give a nano material.
The conventional process for delaminate the layered clay to randomly exfoliated clay takes two main procedures: intercalating the clay with a surfactant and then blending with polymers for the clay exfoliation. In U.S. Pat. No. 6,822,019, the present inventor provided an intercalant prepared by copolymerizing poly(oxypropylene)-amine and polypropylene-grafting-maleic anhydride (PP-g-MA), which is used to intercalate MMT. In U.S. Pat. No. 6,765,050, the present inventor also provided an intercalant prepared by acidifying poly(oxypropylene)-amine to increase the interlayer distance of MMT to an unprecedented range. In U.S. Pat. No. 7,022,299, the present inventor further exfoliating the product of poly(oxypropylene)-amine and PP-g-MA by emulsification and displacement reaction with sodium hydroxide. The exfoliated nanosilicate platelet has a high-aspect-ratio and charge density. Moreover, the present inventor provided an exfoliating agent in U.S. Publication No. 2005-00801805, which is prepared by acidifying product of polymerizing poly(oxypropylene)-diamine and DGEBA. This exfoliating agent can modify the layered clay through only one step.
In the present invention, a hyperbranched polyamine with multiple functional groups is provided as an exfoliating agent. This exfoliating agent can be used to directly exfoliate an inorganic clay such as MMT and Mica through the intercalation and displacement reaction. Further, random form of nanosilicate platelets can be extracted from the product solution.